Radio interference eliminator



May 15, 1934. G. SJOHOLM El AL RADIO INTERFERENCE ELIMINATOR 2 Sheets-Sheet 1 Filed Sept. 25, 1931 Illll'l IIIIIIILI Patented May 15, 1934 I 1,959,114 RADIO INTERFERENCE ELIIVIINATOR Gilbert Sjoholm and Elden Brisbois, Detroit, Mich, assignors to Burroughs Adding Machine Company, Detroit, Mich., a corporation of Michigan Application September 25, 1931, Serial No. 564,990 I 10 Claims.

Our invention relates to radio interference eliminators and is concerned primarily with providing a device of this character which is intended for use in connection with an adding machine electric circuit, although the generic conception involved is readily adaptable in other operating environments.

One object of our invention is to provide an' eliminator or filter for incorporation in an electric circuit comprising a motor and a makeand-break switch which is arranged to substantially prevent the high frequency oscillations set-up by sparking at the switch or brush contacts from being propagated throughthe atmosphere and along the metallic conductors and which would otherwise be picked up by radio receiving apparatus as strays or static.

A further object is to devise a highly compact, filtering unit including condensers and resistance, which is of such a size that it may be readily mounted on the apparatus desired without unduly adding to the total weight, and which is in addition relatively cheap to-manufacture.

A further object is to provide a condensing unit composed of a plurality of inductively related condensers for use in a circuit of the character noted above, one of the condensers being grounded, with a consequent similar condition existing for the unit as a whole and thus effec-' tively preventing any antenna-like action of the circuit with which the unit is associated.

A further object is to devise an effective method of manufacturing a multiple condenser of the type indicated above which is characterized by rapidity, a minimum of handling on the part of the operator, and relatively low cost.

For purpose of illustration, our improved eliminator will be described as applied to the electrical circuit of an adding machine, but-it will be understood that th application of the device is not so limited, as the structure is susceptible of use in other circuits which are subject to frequent interruptions.

It is well known that high frequency oscillations, other than those for which a radio receiving apparatus has been tuned, are received therein as strays or static, thus causing interference and loud crackling noises. Such oscillations travel not only through the air, but also along metallic conductors and it is therefore important to prevent their transmission in electrical circuits which are prone to their creation and which are further used within receiving range of radio apparatus. In an adding machine circuit, for example, these electromagnetic waves proceed from two sources, viz., the sparking between the brushes and commutator of the motor, and that created when the circuit is made or broken by the movement of the switch. The antenna necessary to radiate these oscillations, which are of the order of radio frequency, through space, is provided by the wiring between the motor and the switch and betweenthe switch and wall receptacle, the ground being furnished by the motor and machine housing. At the instant when the spark exists, the wiring on opposite sides thereof becomes charged by these oscillations precisely after the. manner of condenser action exhibited by an actual transmitting antenna under similar conditions. In other words, the indicated circuit functions substantially as a radio transmitting apparatus and it is therefore desirable, not only to prevent these radiated oscillations from reaching a radio receiving set through the atmosphere, but also to prevent those oscillations which are proceeding along the wiring from reaching the same point.

In order to nullify the antenna action of the circuit, it is only necessary to ground both ends thereof and this condition is obtained by providing a ground additional to that furnished by the motor and machine housing. This additional ground is secured through the medium of a grounded condenser which is properly connected in the circuit and which is inductively related to two other condensers, one of which is shunted around the switch and the other is by-passed across the line conductors. These condensers are preferably consecutively wound on each other in order to form a small, compact unit which is readily mountable upon an adding machine.

These and further objects of our invention will be set forth in the following specification, reference being had to the accompanying drawings, and the novel means by which said objects are eifectuated will be definitely pointed out in the claims.

, In the drawings:

Figure 1 is a perspective view, illustrating a portion of an addingmachine with our improved filtering unit mounted thereon and showing generally the size of the filtering unit with respect to the adjacent structure.

Fig. 2 is a sectional, plan view of our 1111- proved interference eliminator.

Fig. 3 is a side elevation of the multiple condenser unit constituting the major portion of the filtering unit, showing the manner of consecutively winding the separate condensers upon each other, it being understood that an actual unit presents a more compact appearance than does the drawing and that the paper insulating strips are discontinuous in this particular form.

Fig. 4 is an electrical diagram showing the re- 5 lation of the individual condensers to the respective portions of the circuit, the condensers being separated in order to more clearly illustrate their functions. Fig. 5 is an electrical diagram showing the individual condensers occupying actual relative positions with respect to the remaining portions .of the circuit.

Fig. 6 is a plan view, partially broken away, of

the strip assembly composed of alternate layers 5 of tinfoil and paper insulation from which the innermost condenser unit shown in Fig. 3 is made.

Fig. '7 is a side elevation showing a modified condenser unit, immediately after winding and before compression, this form differing from that illustrated in Fig. 3 in that the insulating strips are continuous.

Referring to the drawings, the numeral 10 designates a fragmentary portion of an adding machine structure, to which is attached by means of an arm 11 a radio interference eliminator casing 12. Within said casing is disposed a multiple condenser unit 13 which is connected externally of the casing to the electrical circuit of the machine in the manner presently described. In order to prevent the introduction of moisture which would otherwise shorten the life of the eliminator, the casing is .preferably lined with insulating fabric 14 and is filled with sealing compoimd 15 after the insertion of the condenser 3 unit and other parts subsequently described.

Referring to Figs. 3 and 4, the multiple condenser unit is' composed of individual condensers 16, 17 and 18, which are consecutively wound upon each other after'the fashion of a spool. Specifically. the condenser 16 comprises strips of metallic ribbon or tape 19 and 20 which are spaced from each other by an insulating strip 21 formed of paper and the-like. A second insulating strip 22 is disposed beneath the metallic strip 20 so that the assembly is composed of a pile of superimposed, alternating strips of insulation and metallic ribbon. The indicated relation of the several strips is illustrated more particularly in Fig. 6 for the condenser under discussion and it will be especially noted that the width of the insulating strips are somewhat greater than the metallic strips in order to prevent any possible short-circuiting of the me allic strips when the condenser is compressed as hereinafter described. The assembly of strips 19, 21, 20 and 22 is wound upon itself until the desired length is obtained, as dictated by the required capacity of the condenser, whereupon the ends of the several strips are cut in such a manner that the ends of the insulating strips extend beyond the ends of the metallic strips, 2. similar condition having first been effected with respect to the beginning ends of the several strips. The extension of the insulating strip beyond the ends of the metallic strips is also to prevent short-circuiting. As a convenient means of winding the condenser, it is contemplated that the strip assembly will be coiled about a suitable mandrel and after the desired length of the initial condenser has been obtained, certain leads 41 and 40, hereinafter described, are attached to the metallic strips 19 and 20, respectively. Thereupon, the second condenser 17, which is composed of metallic strips 23 and 24, insulated from each other by a paper is then suitably shaped for subsequent insertion the metallic strip 24 in the arrangement of parts shown in Fig. 3, is then wound in the same manner upon the condenser 16 and leads 51 and 37 thereafter connected to the ends of the strips 23 and 24, respectively, as in Fig. 4 presently described. In the same manner, the condenser 18, which is composed of the metallic strips 27 and 28, separated by an insulating ribbon 29, with a second insulating ribbon 30 disposed below the metallic ribbon 28, is then wound upon the condenser 1'7 and leads 52 and 39, presently described, are attached to the ends of the metallic strips 2'7 and 28, respectively, as in Fig. 4. In each of the condensers 1'7 and 18, the ends of the paper strips extend beyond the adjacent ends of the metallic strips, respectively, in order to prevent short-circuiting, as stated in connection with condenser 16. The condenser unit 13 so formed,

Within the casing 12 and the exterior of the unit may be coated with paraffin or any other selected material.

In considering the application of the multiple condenser unit 13 to a typical adding machine circuit, it is convenient to regard the condensers 16, 1'7 and 18 as being separated from each other in a structural sense. Referring then to Fig. 4, the numeral 31 designates the customary make-andbreak switch which is connected by means of a lead 32 to the field coils 33 of a motor 34. the latter in turn being connected by a lead 35 with a suitable source of electrical energy and the switch 31 being connected to the same source by means of a lead 36. Connected around the switch 31' is a shunt circuit consisting of the condenser ribbon 23 which is connected to the lead 36 by the lead 51 and the condenser ribbon 24 which is connected by means of the lead'3'7 to a non-inductive resistance 38 the latter in turn being connected to the lead 32. The condenser ribbon 27 is connected to the lead 35 by the lead 52, and therefore to one of the brushes on the motor 34, while the associated ribbon 28 is grounded by a wire 39 which is fastened to the condenser casing 12 which in turn is grounded to the adding machine 120 proper by a wire 39 (see Figs. 1 and 2). The condenser 16 is bridged across the leads 35 and 36, the ribbon 20 thereof being connected by a wire 40 to the lead 35 and the ribbon 19 by a wire 41 to the lead 36. v 12 In the normal operation of the circuit illustrated in Fig. 4, the sparking occurring at the contacts of the switch 31 and at the brushes of the motor 34 would ordinarily set up high. frequency impulses that would be, directly radiated 3 through the atmosphere, the adjacent circuit portions functioning substantially as an antenna, and such oscillations would also proceed directly along the circuit As stated above, the antenna action of the indicated portions of the 135 circuit can be completely prevented if both ends thereof are grounded and, in the present instance, one ground is afforded by the motor and adding machine housing, while the other ground is furnished by the condenser ribbon or layer 28.

With respect to the oscillations which proceed directly along the wire, and considering those set up by the sparking at the switch contacts, the non-inductive resistance 38 serves to greatly suppress the extent of the arc created by the move- 145 ment' of the switch 31 to a circuit interrupting position and the spark which is actually formed charges the condenser ribbons 23 and 24. When the switch 31 is again closed, the charges on the strip 25, with a second paper 26 disposed below vribbons 23 and 24 are partly short-circuited by1 the switch itself and the remaining portion of the charge is short circuited through the condenser ribbons 19 and 20 which are inductively grounded by the condenser ribbons 27 and28. The oscillations set up by the commutator and brushes of the motor are grounded directly through the condenser ribbons 27 and 28.

The foregoing condenser arrangement provides a very convenient method for stopping or filtering high or low frequency currents as desired, for considering the high frequency oscillations which proceed directly along the wiring, the inductive reactance of the motor field coils which varies directly with the impressed frequency, is of sufiicient amount to entirely obstruct any passage of such oscillations in one direction, while their passage in the opposite direction is readily permitted by the low capacitive reaction of the condenser unit, for the high frequency involved, directly to the ground. On the other hand, the reactances of the several condensers are sufliciently high for the relatively low frequency of the impressed electromotive force on the main circuit to completely prevent any tendency of the alternating current to move by way of the condenser by-pass rather than through the intended circuit formed by the motor and switch.. One of the particularly novel features of our invention is the structure of the multiple condenser unit, whereby the component condensers are inductively related, with one of the condensers being directly grounded and thus insuring a common ground for all condensers.

In the actual manufacture of the multiple condenser unit, certain structural simplicities may be adapted over the relation illustrated in Fig. 4. In the latter instance, it will be observed that a total of six connections is necessary to incorporate the three condensers in the electric circuit, but owing to the fact that the condenser'ribbons 20 and 27 are connected to the same power lead 35 and that the condenser ribbons 19 and 23 are connected to the same powerlead 36, it is possible to take advantage of this condition (see Fig. 5) by connecting the condenser ribbons 20 and 27 internally of the principal condenser unit by means of a lead 42, and the condenser ribbons 19 and 23 internally by means of the lead 43, so that a total of only four leads 3'7, 39, 40 and 41 project from the condenser casing 12, thereby eliminating the leads 52' and 51 shown in Fig. 4.

' This construction serves to materially simplify the unit as a whole and to eliminate considerable wiring. I

In Fig. 7 is diagrammatically illustrated a method of winding the multiple condenser hereinabove described which is characterized by certain important advantages in respect of rapidity and a minimum of handling on the part of the operator. According to this method, a stripassembly composed-of paper insulating strips 45 and 46 alternately arranged with respect to metallic ribbons 47 and 48 is first formed in the manner generally outlined above, the length of the assembly being determined by the capacity requirement of the multiple condenser unit. The assembly so formed is then wound about a mandrel 49 in successive convolutions until the desired size of the innermost condenser is attained. Thereupon, the

operator cuts a piece of appropriate length from each of the metallic ribbons to thereby determine the ends of such ribbons for the innermost condenser, but without cutting the insulating paper strips. Winding is then resumed until the second condenser is formed, whereupon the metallic ribbons are again out in the same manner to form the second condenser and so on for the number of condensers in the unit. This modification accordingly differs from that illustrated in Fig. 3 in that the insulating paper strips are continuous and thus afford a convenient holding and retaining means which greatly facilitates the building up of the condenser assembly. In either modification, it will be understood that neither the size of the multiple condenser, nor the component condenser units, are material to the subject matter of the present invention, as these sizes and capacities will vary dependent upon the characteristics of the circuits with which employed.

While we have shown one set of elements and combinations thereof for effecting our improved radio interference eliminator,- it will be understood that the same is intended for purpose of illustration only and in no wise to restrict our device to the exact forms and structures shown, for many changes may be made therein without departing from the spirit of our invention.

We claim:

1. The combination of an electric circuit comprising a make-and break switch and a motor,

and a radio interference eliminator in the form of a multiple condenser unit comprising a plurality of individual condensers inductively positioned' with respect to each other and connected, respectively, to said switch, motor, and for bridging across the line conductors to include said switch and motor, said motor condenser being grounded.

2. The combination of an electric circuit comprising a make-and-break switch and a motor, and a radio interference eliminator in the form of a multiple condenser unit comprising an arcabsorbing condenser shunted around said switch, a grounding condenser connected to said circuit, and a' by-pass condenser bridged across the line conductors of said circuit to include said switch and motor, said condensers being consecutively wound on each other to make a small, compact mass.

3. The combination of an electric circuit comprising a make-and-break switch and a motor, and a radio interference eliminator in the form of a multiple condenser unit comprising an arcabsorbing condenser shunted around said switch, a grounding condenser connected to said circuit, and a by-pass condenser bridged across the line condensers of said circuit to include said switch and motor, said condensers being inductively positioned with respect to each other.

4; The combination of an electric circuit comprising a make-and-break switch and a motor,

wound on each other to make a small, compact mass and being inductively positioned with respect to each other.

5. Thecombination of an electric circuit comprising a make-and-break switch and a motor,

and a radio interference eliminator in the form of a multiple condenser unit comprising an arcabsorbing condenser shunted around said switch,

a grounding condenser connected to said circuit, and a by-pass condenser bridged across the line conductors of said circuit to include said switch and motor, said condensers being consecutively wound on each other to make a small, compact mass and being inductively positioned with respect to each other, the layers of said by-pass condenser being connected internally of. said unit to a layer of said arc-absorbing condenser and a layer of said grounding condenser, respectively, whereby a total of four leads project externally of said unit.

6. The combination of an electric circuit comprising a plurality of electrical devices characterized by spark emission when operated, and a radio interference eliminator in the form of a multiple condenser unit comprising a plurality of individual condensers inductively positioned with respect to each other and connected to said devices, respectively, and for bridging acrossthe line conductors to include said devices, one of said condensers being grounded.

7. The combination of an electric circuit comprising a plurality of electrical devices characterized by spark emission when operated, and a radio interference eliminator in the form of a multiple condenser unit comprising a plurality of individual condensers inductively positioned with respect to each other and connected to said devices, respectively, and for bridging across the line conductors to include said devices, one of said condensers being grounded and all of said condensers being consecutively wound on each other to form a small, compact mass.

8. The combination of an electric circuit comprising a make-and-break switch and a motor, and a radio interference eliminator in the form of a multiple'condenser unit comprising a plurality of individual condensers inductively positioned with respect to each other and connected, respectively, to said switch, motor and for bridging across the line conductors to include said switch and motor, one of said condensers being grounded.

9. The combination of an electric circuit comprising a, make-and-break switch and a motor, and a radio interference eliminator in the form of a multiple condenser unit comprising a plurality of I individual condensers connected, respectively, to said switch, motor, and for bridging across the line conductors to include said switch and motor, one of said condensers being grounded and all of said condensers being consecutively wound on each other to form a small, compact mass.

10. The combination of a pair of electrical devices characterized by spark emission when operated, and a radio interference eliminator in the form of a multiple condenser unit comprising a plurality of individual condensers inductively positioned with respect to each other and connected, respectively, to said devices and for bridging across the line conductors to include said devices, one of said condensers being grounded and all of said condensers being consecutively wound on each other to form a small, compact mass, the layers of said bridging condenser being connected internally of the unit to a layer of each of said other condensers, respectively,

whereby a total of four leads project externally of said unit.

GILBERT SJOHOLM. ELDEN BRISBOIS.

CERTlFlGATE or CORRECTION.

Patent No. 1,959,114.

May s, 1934.

GILBERT SJOHOLM, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as fol-lows:

"condensers" read conductors; condensers;

Page 3, line 126, for

I and line 137, claim 4, for "conductors" read and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Off ice.

Signed and sealed this 19th day of June,

(Seal) Bryan M. "Battey Acting Gommissioner of Patents. 

